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Joshy

Posted 10 October 2016 - 01:53 PM

Sagacious

Posted 10 October 2016 - 01:54 PM

Sagacious

Administrator

Administrators

87 posts

A set of EOL resistors is included with the M1.

EOL resistors make it possible for the alarm panel to monitor the integrity of the wiring for each zone circuit. Without EOL resistors, the panel would normally see a short circuit when the contact switch for a door or window is closed, and an open circuit when the door or window is open.

The problem is that if the wiring develops a short between the wires for some reason, the alarm panel can no longer tell when the door/window is opened. It would look closed all the time, and someone could walk right in and the alarm would never go off.

With the EOL resistor, a short would look different from a closed or open contact switch, allowing the panel to report a trouble condition.

EOL resistors are also used to monitor the integrity of wiring for smoke detectors and siren/bell circuits. These are sometimes different value resistors from the zone EOLs.

Sometimes, an installer will place the EOL resistors at the panel, rather than at the far end of the zone wiring. Placing them at the panel is the wrong way to do it, and they provide no supervision that way. Always put them at the far end of the wire, at the last contact in the zone.

Joshy

Posted 10 October 2016 - 01:55 PM

Home Automation

Posted 10 October 2016 - 01:56 PM

Home Automation

Member

Members

26 posts

Awesome thanks

Ground fault. If on the high side of the zone, a ground could bridge and complete the circuit. Common occurrence at a local university here when they were running 3 state EOLR's. Ground fault or a moderate resistance bridge to ground (aluminum extrusions with fished conductors are notorious) can cause enough for the loop to set up but have a high resistance ground fault. Also depends on the reference your system has.

Posted 10 October 2016 - 01:57 PM

Home Automation

Posted 10 October 2016 - 01:57 PM

Home Automation

Member

Members

26 posts

Depends on the nature of the fault. If the resistor is on the high side, you could have a short to ground that completes the circuit, such as the aluminum extrusion of a storefront and building steel....the variable is whether or not the low side of the zone gets a ground reference or not. Same issues occur on fire alarms with cabling. Two ground faults essentially equals a short circuit on the same loop. If you have a powered detector, that's even worse as you have 2 locations you can get a ground or external reference.

Think of it on a zone with multiple contacts wired in series. If you have wiring between them and a short on the high leg to ground, you effectively shunt all the downstream contacts and the panel never sees them.

Back in the old Logiplex access control days (and security systems) at a local university, they had multiplex zones on a single cable pair. Enough high resistance faults or a ground or two, you could open up one of the zones and the panel would never see it (part of why I hate zone "doubling" on panels).

Easiest way would be to think of it in automotive terms, where is the ground of a typical car located? Is there one or can I pick it up almost anywhere?